Beneath the Surface: Diatoms of the Bay

From May, 2009 Newsletter

by Brittany Sabol, Education & Training Director


Floating in the waters of the San Francisco Bay is a veritable smorgasbord of yummy treats – that is if diatoms are your idea of fine dining.  Diatoms are a major component of plankton, which consists of all of the tiny organisms that drift along with the current.

Diatoms are an important part of the food web in the San Francisco Bay.  They are a producer, making their own food through photosynthesis with yellow-brown chlorophyll (which is different from the green chlorophyll of most plants). Studies estimate that diatoms are responsible for 20-25% of all carbon fixation (photosynthesis, shell-building, etc.) on the planet.  A variety of species prey upon diatoms including small fish, clams, and other invertebrates.

Diatoms are microscopic single cell organisms that can also form large visible colonies.  They have a cell wall called a frustule made of silica (the main component of most forms of glass).  The cell wall has two valves that fit together like a Petri dish with one nesting into the other.  To reproduce, the valves separate and each one grows a new smaller valve.  This process results in ever shrinking cells.  When they become too small, they reproduce by forming an auxospore, a specialized cell that results in a new large cell.

Water quality studies often use diatoms as a measurement standard as their abundance varies with the quality of the water.  When diatoms are more abundant the rest of the aquatic ecosystem is also likely to be doing well.

When we are walking in the salt marshes or sailing out on the bay, we often only think of the species we can see, the birds, or fish.  Next time take a moment to think about the tiny diatoms that help support the ecosystem of our beautiful bay.